Conventional support systems for blinds have included flat walled extrusions within which a carrier travels while supporting a wall covering member. In the case of vertical blinds, each carrier supports a vane in a particular orientation. The carrier provides the structure for controlling the orientation of the vane, as well as providing for the movement of the vane along the track. It is the track which has been formed as a flat walled extrusion within which the carrier must travel.
The carrier also rides about a vane orientation control rod which ideally lends no support to the vane. The rod is rotatable about its axis to operate a gear mechanism in the carriers to cause the vanes to change their angular position. The carriers further have an expandable and contractable connection with each other which enables the carriers to spread out to an optimum spacing when the blinds are covering the window, and move in to a close spacing when opened to uncover the window. This is usually controlled by a cord and is independent of the control for adjusting the angular position of the vanes.
The carrier usually consists of a rectangular member having a pair of side wheels for riding in the raceway of the extrusion. The wheels typically have a clearance with a vertical wall adjacent their outer radial surface. Although the carrier is not completely free to turn within the raceway of the extrusion, the needed relatively loose clearance enables the carrier to have some ability to turn.
Where the turning is sufficient, the wheels at their mid level height will contact and rub against the vertical wall of the extrusion. The friction generated by the rubbing of the wheel against the vertical wall is worsened since it has several components. First, the carrier is being dragged on both sides as it travels across the track. From one wheel the front mid level of the wheel is dragged and from the other the rear mid level of the wheel is being dragged.
Secondly, the wheels may still try to turn to the extent that they still engage the bottom race of the track by virtue of the weight of the vane. In essence, the wheel is being dragged against the vertical wall while it is still being turned by virtue of its contact with the bottom track of the raceway within which the wheel is supposed to fit. Thirdly, as the wheel is compressed against the vertical wall of the track on one side of the wheel, the other side of the wheel is jammed against the carrier, further impeding the ability of the wheel to turn.
Fourthly and most importantly, since the carrier has a relatively close width tolerance against the raceway, the turning of the carrier causes it to "jam" within the track. Where the carrier jams, a significant amount of width forces are exerted against the track. Where the forces are strong enough, such forces can cause failure in other structures within the track, and particularly with the structures which actuate movement of the carriers along the track.
Close tolerancing with regard to the wheels and the raceway in which they operate cannot be significantly compromised. An increase of the width of the wheels would make the system bulky, and would introduce further friction in the wheel design. Allowing too much play in the width would allow the wheels to ride from side to side, and would at worse enable the carrier to come off track and fall through the extrusion. Even though the vane angle control rod would prevent a total drop out, even a partial drop out would cause jamming or would place unacceptable pressures on the vane angle control rod.
What is therefore needed is a track which eliminates many of the problems associated with jamming and increased resistance to travel across the window. The needed system would compromise none of the advantages of the existing devices, yet offer more reliability and trouble-free operation.